On Fri, 17 Aug 2007 18:26:31 +0700, wrote:

Here's a little engineering insight. If a drive shaft is lightened
by drilling out an axial hole whose diameter is one half the outer
diameter - the shaft's strength in torque is reduced by 5% and its
weight is reduced by 25% This is important in aircraft
construction.

Driveshafts are usually tubes and not rods. Always for cars and big
ships. It is only the smaller boats that lack the space.

Casady

Richard Casady wrote:

On Fri, 17 Aug 2007 18:26:31 +0700, wrote:

Here's a little engineering insight. If a drive shaft is lightened
by drilling out an axial hole whose diameter is one half the outer
diameter - the shaft's strength in torque is reduced by 5% and its
weight is reduced by 25% This is important in aircraft
construction.

Driveshafts are usually tubes and not rods. Always for cars and big
ships. It is only the smaller boats that lack the space.

Casady

uh what have you been taking?
drive shafts on cars are tubes may be on other things; i have only seen one
driveshaft on a boat that was tube and it corroded til it fell apart.
mostly you find a ss shaft machined to speck for the boat and the power out
put of the engine.

but go ahead and use spring steel tube drive shafts it will give me
business.

On Fri, 17 Aug 2007 02:13:06 GMT, Brian Whatcott
wrote:

On Thu, 16 Aug 2007 09:59:09 -0700, Frogwatch
wrote:

I will defend my suggestion although it sounds impractical for the
Alberg. A coupler properly made...


Here's a little engineering insight. If a drive shaft is lightened
by drilling out an axial hole whose diameter is one half the outer
diameter - the shaft's strength in torque is reduced by 5% and its
weight is reduced by 25% This is important in aircraft
construction.

So as applied to cutting and shutting a propellor shaft, if its
diameter is x, and it is cut then bridged with a coupler,
the coupler's diameter ought to be just over twice the shaft's
diameter, to bridge across the gap.
....
Brian Whatcott Altus OK


I knew, sure as sure, as soon as I wrote "engineering insight" there
would be a screw-up. And there was.
If you want to maintain torque capacity though a coupling, it doesn't
need to be TWICE the shaft diameter. That's three times the cross
section area, at about twice the distance from the axis.
The coupler diameter doesn't need to be even 1.5 times the diameter
of the shaft. 1.3 times the shaft diameter would do it.
So a coupler whose diameter is about one inch bigger than the shaft
could handle up to a three inch shaft, if well connected. Yeah Baby!

Brian W

On Tue, 14 Aug 2007 09:14:49 -0500, "KLC Lewis"
wrote:


"Roger Long" wrote in message
...

"Frogwatch" wrote

Cut the prop shaft in the boat. Take out a 2" long section. Take off
prop. When re-installing, use a sliding coupler to join the two
pieces. This assumes you even have enough room to do this cutting.


Woah! This is up there with some of the worst advice I've encountered on
this newsgroup.

--
Roger Long


Ya, I kinda cringed when I read it. Alignment questions aside, that would
have to be one strong coupler.
Why? Isn't that just a twenty five horse motor? This is a boat, not an
electrical generating station.

Casady

Jonathan W wrote:
I bought an Indigo 3 bladed prop last week for my Alberg 35 with the
original Atomic 4, as the existing prop succumbed to electrolysis

I went down to the boat yesterday, worried that I might not be able to
loosen the old hub's grip on the shaft. It was also a 3 bladed prop.
That was actually easy after about 5 minutes with a map gas torch.

I seem to have only about an inch of space between the end of the prop
shaft and the rudder (post). The hub is about 2-2,5 inches thick. I've
tried swinging the rudder from stop to stop, but don't seem to be able
to find an angle that will allow the old prop to come off, or, for that
matter, a new one to go on.

Others must have encountered this problem and found a solution.....

At this juncture it seems to me that I either have to dismount the
rudder to gain an extra inch or so, or I have to unmount the engine and
pull the prop shaft forward a couple of inches (if that's even possible )

I am hoping that I missed something perfectly obvious as I was working
late and was tired.... any help appreciated.

Thanks,

Jonathan Wye



Well, the m marina figured it out. Apparently with enough patience one
could align the prop and rudder and "turn" it off. I had thought
something like this might be the case, as I was tired and it was late
when I got to the prop last weekend.

Also, some years ago I got hit by a Mack truck (literally) and sometimes
I have trouble with certain 3 dimensional space/configuration problems.
This might have been a bit of that, too.

In any event, the new prop is on, and the boat is back in the water.
Wish I could have gotten down this weekend to try it out.

thanks for all the interesting commentary

Jonathan

--
I am building my daughter an Argie 10 sailing dinghy, check it out:
http://home.comcast.net/~jonsailr

Jonathan W wrote:
Jonathan W wrote:

I bought an Indigo 3 bladed prop last week for my Alberg 35 with the
original Atomic 4, as the existing prop succumbed to electrolysis

I went down to the boat yesterday, worried that I might not be able to
loosen the old hub's grip on the shaft. It was also a 3 bladed prop.
That was actually easy after about 5 minutes with a map gas torch.

I seem to have only about an inch of space between the end of the prop
shaft and the rudder (post). The hub is about 2-2,5 inches thick.
I've tried swinging the rudder from stop to stop, but don't seem to be
able to find an angle that will allow the old prop to come off, or,
for that matter, a new one to go on.

Others must have encountered this problem and found a solution.....

At this juncture it seems to me that I either have to dismount the
rudder to gain an extra inch or so, or I have to unmount the engine
and pull the prop shaft forward a couple of inches (if that's even
possible )

I am hoping that I missed something perfectly obvious as I was working
late and was tired.... any help appreciated.

Thanks,

Jonathan Wye



Well, the m marina figured it out. Apparently with enough patience one
could align the prop and rudder and "turn" it off. I had thought
something like this might be the case, as I was tired and it was late
when I got to the prop last weekend.

Also, some years ago I got hit by a Mack truck (literally) and sometimes
I have trouble with certain 3 dimensional space/configuration problems.
This might have been a bit of that, too.

In any event, the new prop is on, and the boat is back in the water.
Wish I could have gotten down this weekend to try it out.

thanks for all the interesting commentary

Jonathan

I'm glad you found a solution. Having said that, what year was all of
this assembled? Maybe removing the rudder, looking for corrosion on the
pieces and giving everything as good cleaning and greasing would be a
good idea.